In the study of the metabolism of calcium and phosphorus, not only are the absolute retentions of these elements of importance, but of almost equal significance is the relation between the amounts of these elements retained. From the total amounts retained, rough standards of the minimal retentions desirable for normal growth have been attained. Through an understanding of the ratio of retained calcium and phosphorus, a better interpretation of the type of metabolism in the child studied may be realized.
Of the calcium retained by the body, from 97 to 98 per cent is utilized in the formation of bone; the remainder is found in the body fluids. For practical purposes, the retention of calcium can thus be used as an index of the rate of the growth of bone. Phosphorus, on the other hand, is utilized not only by bone, but also by the soft tissues, particularly the muscles,